What is Genetics?
The study of how traits are inherited.
Heredity: The passing of traits from one generation to the next.
Traits: Characteristics
How can we determine the frequency of a trait in offspring?
Gregor Mendel: Father of Genetics. Discovered the basics of heredity
Mendel worked with Pea Plants
He concluded that each trait is controlled by "Two Factors" (genes), one from each
parent.
Genes are short sections of chromosomes
(They control which traits are expressed in an organism)
Alleles : different forms of a gene that exist in a population. Some alleles
can be dominant over other alleles
Mendel Law of Dominance:
When organisms pure for a trait are crossed, all their offspring will show the
dominant trait.
The trait that was expressed is dominant, while the trait that did not
show up was called recessive
Parent generation
Tall x Short
F1 Generation
all plants are Tall
Recessive:
A trait that is covered over.
Hidden when the other copy of the gene contains the dominant allele.
It shows up only when there is no dominant allele present
lower-case letter (t)
Dominant
A trait that covers over another form of that trait
Always shows up
capital letter (T)
Phenotype: The physical appearance of an organism
Genotype: The genetic makeup of an organism
Phenotype is:
Brown hair
Genotype can be:
Bb or BB
B: Brown
b: blond
For a recessive trait to show their appearance in an offspring, both
recessive alleles must be present in an individual
Blond genotype is bb
Tall Plant (TT) x short plant (tt)
All offspring are Tall Plants (Tt)
Homozygous or pure; alleles for a trait are the same Ex: TT or tt
Heterozygous (hybrid): alleles for a trait are different Ex: Tt
Cross the F1 generation to itself.
F2 ¼ are short , ¾ are tall.
Punnet Squares: a technique used to help determine the possible
frequency of a trait in offspring
Example: Pea Plant TT X
Let T= Tall allele (gene)
Let t= short allele (gene)
Pea Plant tt
What is the phenotype of all the offspring?
What is the genotype of all the offspring?
Incomplete Dominance:
When neither allele for a gene follows the dominant/recessive pattern
The organism shows a trait that is an intermediate phenotype.
Example:
The gene for the color of some flowers has one allele for red and one
for white. When both alleles are present, neither is dominant, and the
flower color is pink. Cross:
WW x RR all F1 will be WR(Pink)
Polygenic Inheritance
Occurs when a group of gene pairs acts together to produce a trait
The effects of many alleles produces a wide variety of phenotypes
Ex: eye color, height, and skin color are produced by a combination of
many genes.
The impact of the environment on genes
The environment affects the expression of genes.
Ex: Himalayan rabbits: the dark-colored fur allele is able to express only at
low temp.
Multiple Alleles:
A trait that is controlled by more than two alleles is said to be
controlled by multiple alleles
Traits controlled by multiple alleles produce more than three
phenotypes of that trait
Example:
The alleles for blood types in humans are:
 A, B, and O
The O allele is recessive to both the A and B alleles
Genotype
AA or Ao
BB or Bo
AB
oo
Phenotype
A
B
AB
O
Sex Determination
Sex Linked Inheritance
There are more colorblind males than females?
There are more male hemophiliacs than female?
There are more males with muscular dystrophy than females?
Recessive traits that are carried on the X chromosome, only need one copy
in males to express themselves.
Males (XY)
Females have two X chromosomes and therefore both must carry the
recessive allele to be expressed
Female (XX)
Do these crosses using the Punnet Square for color blindness
Cross: XY(normal male) x XXc female carrier for color blindness
1) Colorblind male
Xc Y
x
Normal female
XX
2) Colorblind male
Xc Y
x
Female carrier
Xc X
3) Normal Male
XY
x
Colorblind female
Xc Xc
RECESSIVE GENETIC DISORDERS
Sickle Cell Anemia: abnormally shaped red blood cells that can not
function properly. Oxygen can not reach tissues.
Cystic Fibrosis: Homozygous recessive disorder. Thick mucus builds up
in the lungs and makes it hard to breath
Human Genome
Identify genes responsible for specific traits
Be able to begin treatment of disorders while children are young
and save lives of people at risk.
Why do we study Pedigrees?
See packet
Karyotyping: Enlarged photograph of the pair chromosomes undergoing
mitosis. Show missing or extra chromosomes.



HUMAN GENOME
Tracking human genes:
Chromosome map representing all of the human genetic material or chart
that shows the location of individual genes on a chromosome
Identify genes responsible for specific traits
Be able to begin treatment of disorders while children are young and save
lives of people at risk.
Why would such gene map be useful?
More than 3000 human disorders are inherited: cancer, huntington's
disease, cystic fibrosis etc...
Developing a map of these genes is the first step towards diagnosing